A newborn baby was found dead in a patch of grass yesterday outside a Bronx housing project, and police are investigating whether it was thrown out a window by the mother.

The girl may have been tossed from the fifth story by a teen, who went to school afterward, police sources said. The body was found lying face down outside Eastchester Gardens houses in Williamsbridge at 7:30 a.m. by building-maintenance workers.

Police sources said a 14-year-old who lives on the fifth floor of the building gave birth to the 7-pound, 6-ounce infant.

Cops used dogs to track the scent of the tragic tot to the teen’s apartment.

She was eventually picked up by police and brought to Jacobi Hospital for tests.